How Composite Decking Works


Newly built deck on rear of house.
Newly built deck on rear of house.
iStockphoto.com/Eric Honeycutt

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­It used to be much easier to decide how to construct a deck. Did you want to make it out of wood -- or wood? Nowadays, there's a vast array of decking available, and some of it doesn't even have a trace of wood in it. Why all the options? It's part of our never-ending quest to make things better, easier and more c­onvenient.

The common denominator in wood decking, whether it's treated pine, redwood or cedar, is the need for regular care and maintenance. Sanding, staining and resealing are an annual chore for some, but others might go two or three years between treatments.

In recent years some sharp entrepreneurs, recognizing that many homeowners might appreciate a lower-maintenance option, came up with some alternatives. In addition to vinyl and aluminum, there's even plastic decking available now. But the segment of the decking industry that's seen the biggest change is what's called composite decking.

Composite decking is typically made from a combination of different materials (namely, wood and plastic), which are processed to give the appearance of wood. Both the wood (which consists of lumber industry byproducts like sawdust, chips and wood fiber) and the plastic can be made from virgin or recycled material [source: Jones].

Manufacturers mix the components, often adding a pigment and preservative. The mixture is heated, formed into board-shaped lengths and then cooled. The resulting board of composite decking is usually heavier than wood but not as strong. But composite decking is resistant to rot, doesn't warp, won't giv­e people splinters, and doesn't need to be painted, stained or sealed.

The color of most composite decking will fade somewhat after the initial installation. Homeowners are encouraged to keep their composite decking swept clean, attend to any stains as soon as possible, and hose it down twice a year, finishing with a soap and water scrub [source: Decks].

Head over to the next page to read about the different types of composite decking.

Types of Composite Decking

Hate making decisions? Well, lucky for you there are only two types of comp­osite decking on the market: solid and hollow. Solid looks more like wood and is heavier than the hollow version. Because of its greater mass, solid decking will expand and contract more with temperature fluctuations.

Hollow composite decking has a more man-made look. However, it won't expand and contract as much as solid composite decking. You need to be careful when handling it, though, because it's more susceptible to damage before it's installed. Solid composite decking is more popular because of its superior strength and closer resemblance to real wood [source: Montenegro].

Regardless of the type of composite decking, it's important that the product is treated with a preservative and antifungal chemical. When left untreated and exposed to the elements, most wood will rot over time. Excessive moisture accelerates the rotting process. Even though the wood fibers and other cellulose in the decking have been combined with plastic, it can still rot, according to the Forest Products Journal. Considering that most composite decking products consist of at least 40 percent wood (sometimes as much as 70 percent), the lack of a preservative could cause serious problems. And some composites have wood contents as high as 70 percent [source: Carter].

The preservative is mixed in with the wood during the manufacturing process. Some preservatives, like zinc borate, can remain active in composite decking for more than 20 years.

Composite Decking Material

There are three types of composite decking material: polyethylene-based, polypropylene-based and nonwood plastics. Oil-based polyethylene and polypropylene composite decking contain some wood. The industry seems to be moving away from polyethylene-based composites to focus on the polypropylene-based product (which is typically stronger and less susceptible to expansion and compression) or polyvinyl chloride (PVC)-based product. These plastic­s have no wood content, do not stain or absorb water. Technology is enabling manufacturers to give all these composites a look and feel that approximates real wood. [source: Descoteaux].

A variety of factors come into play when you're choosing the material for a composite deck, such as cost, availability of color and a hidden fastener system. Composite decking is more expensive than wood, but how much depends on the particular product. Nonwood plastics are significantly more expensive than real wood, are lighter than the other composites, and typically don't contain any recycled content.

The color and desired textures of the deck, where the deck is located and how the deck will be used will help narrow down which the best product [source: Decks].

Some of the big manufacturers are ChoiceDek, EON, Epoch Evergrain, GeoDeck, LP Weatherbest, TImberTech, Trex and Veranda. The industry is evolving, with efforts being made to eliminate some of the stain, fading and mold issues that composite decking has been known for. Here are details on some of the products:

  • CorrectDeck is made from hardwood fiber and polypropylene, with 80 percent of its content from reclaimed or recycled material. Its CX line has a top layer of polypropylene that encases the decking with antimicrobial protection to help resist mold and mildew. [source: Descoteaux].
  • Cross Timbers composite is made from oak and polypropylene for a stronger board, which can span 24 inches on center, further than most composite decking
  • GeoDeck's Tongue & Groove includes cellulose with lower amounts of lignin, which makes the product fade-resistant.
  • Veranda's decking has a different combed finish on each side of the board, giving buyers two looks to choose from.
  • EON is 100 percent plastic. The manufacturer uses ultraviolet light inhibitors to eliminate fading. The product has a T-clip to fasten the decking, not nails or screws, giving the finished deck a clean look.
  • Epoch Evergrain looks more like wood than other compression decking, thanks to the use of compression molding to form the product, giving it a deep grain.
  • ChoiceDek's polyethylene and recycled wood decking is lighter and stiffer than some others because of a ribbed design that allows more air circulation between the decking and framing.
  • Many decking companies offer hidden fasteners that are easy to install. Latitudes Composite Decking uses a hidden fastener system that automatically spaces boards with the proper gap [source: Montenegro].

For particulars about installing composite decking, read on.

Building a Composite Deck

While the materials for a composite deck are more expensive than most wood, installation costs are fairly comparable. The same foundation of pressure-treated wood is used for both wood and composite decks, but there are several differences between the way wood and composite decking is gapped and supported.

Note: There is now a plastic lumber, USPL's TriMax, which can be used for structural applications. However, unless accommodations are made to oversize the joists and/or space them more closely, the deck can be bouncy [source: Hardy].

Manufacturer's specifications will guide the size of the gaps required for the composite decking. Gapping (between boards and between the decking and an abutting wall) is necessary to accommodate the expansion and compression that is inherent in composite decking. To determine ho­w many fasteners you'll need for a deck installation, multiply the number of joists by the number of decking boards.

Composite decking is weaker than wood. Installing a composite deck on a foundation originally used for a wood deck will require more joists. You'll also have to adjust the framing if the decking is installed in a pattern, like a herringbone or tile pattern [source: Hardy].

Drainage and airflow are crucial to keeping composite decking from degrading. To install composite decking over a solid surface, you need to build a sleeper system. The surface below the deck needs to be pitched for drainage or outfitted with a gutter system, such as TimberTech's DrySpace Drainage System, designed to drain the water from underneath the decking.

Also, the type of composite decking will dictate certain parts of the installation. For hollow decking, you need to use a picture frame design or a starter strip. The starter strip covers the end of the first piece, hiding the fact that it's not solid. Hollow decking also needs a screw at every junction where a joist meets the decking board [source: Descoteaux].

One final note: While most composite decking manufacturers offer warranties on their products, the warranty will be void if the installation does not precisely follow the manufacturer's directions, because a bad installation can result in a degraded, unsafe deck.

To learn more about composite decking, visit some of the following sites.

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Sources

  • Carter, Tim. "Composite Decking." Ask the Builder. (Accessed 12/14/08) http://www.askthebuilder.com/551_Composite_Decking.shtml
  • Consumer Product Safety Commission. "CPSC, Kadant Composites Inc. Announce Recall of Certain GeoDeck Decking and Railing Material." (Accessed 12/14/08) http://www.cpsc.gov/CPSCPUB/PREREL/PRHTML05/05247.html
  • Decks.com. "Composite Decking Materials Review." (Accessed 12/14/08)http://www.decks.com/article10.aspx
  • Descoteaux, Mike. Marketing Manager, CorrectDeck. Interview 12/15/08.
  • Hardy, Benjamin. "Wood Deck Alternatives." (Accessed 12/14/08) http://www.bobvila.com/HowTo_Library/Wood_Deck_Alternatives-Deck-A2111.html
  • Jones, Rob. "Composite Decking: The Smooth Choice in Decks." Amazines. (Accessed 12/14/08) http://www.amazines.com/article_detail.cfm/517783?articleid=517783&title=composite%2Cdecking%2Ccomposite%2Cdecks%2Cdecking%2Cdecks
  • Montenegro, Margaret. "Composite Decking - The New Trend of Decks." (Accessed 12/14/08)http://www.doityourself.com/stry/compositedecking